
<meta charset="UTF-8">
<style>
    *{
        padding: 0;
        margin: 0;
    }
    ul{
        width: 400px;
        height: 200px;
        background-color: cornflowerblue;
        
    }
    ul li{
        width: 400px;
        height: 30px;
        margin: 20px 0px;
        background-color: darkgray;
    }
    .tip{
        width: 100px;
        height: 30px;
        line-height: 30px;
        text-align: center;
        background-color: red;
        color: white;
        position: absolute;
        border-radius: 5px;
        
    }
    .tip .tip-bottom{
        position: absolute;
        width: 0;
        height: 0;
        top:30px;
        left: 40px;
        border-left: 10px solid transparent;
        border-right: 10px solid transparent;
        border-bottom: 10px solid transparent;
        border-top: 10px solid red ;
        
    }
</style>


<ul>
    <li>01</li>
    <li>02</li>
    <li>03</li>
    <li>04</li>
    <li>05</li>
</ul>
<div class="tip" style="display: none;left:0;top:0;">
    这是提示框
    <div class="tip-bottom"></div>
</div>
<script src="./demo2.js"></script>